This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hawaiian box jellyfish (Carybdea alata) belong to the most notoriously toxic class of jellyfish, the cubozoans, which are commonly found in tropical and subtropical waters from Hawaii to Australia. Cubozoan stings are extremely painful and result in potentially life-threatening Irukandji syndrome, which presents as a constellation of systemic signs and symptoms, including cardiopulmonary distress. A retrospective clinical analysis of emergency room patients demonstrates that Irukandji syndrome occurs in about 5% of local box jellyfish sting victims. Still, the precise biochemical basis for this syndrome is unclear. In Hawaii, Australia and Indonesia, current therapy is limited to symptomatic care. This research proposal is prompted by our recent discovery of small molecules, chemically similarly to certain insect toxins, which induce multiple physiological effects including profound cardiac effects in both crayfish and mice. The specific aims of this project are to conduct focused efforts to purify, identify and physiologically characterize these highly cardioactive compounds. The overall goal is to provide much-needed insights into the mechanisms of action of these compounds and provide the basis for better clinical management. The specific aims of the proposed research are: Specific Aim 1. Biochemical separation of cardioactive compounds Specific Aim 2. Biophysical characterization of cardioactive compounds Specific Aim 3. Physiological characterization of cardioactive compounds The identification and characterization of cardiotoxins and the elucidation of their mechanisms of action should provide insights into the development of more specific and effective clinical-management modalities.